Preparation of 2-chlorobutadiene-1, 3



Patented Feb. 4, 1947 2,415,294 PREPARATION OF 2-CHLOROBUTADIENE-L3 Arthur A. Levine and Oliver W. Cass, Niagara Falls, N. Y assignors to El. du Pont de Nemours & Company, Wilmington,

ration of Delaware 13121., a corpo- No Drawing. Application May 22, 1940, Serial No. 336,625

8 Claims. (01. 260655) This invention relates to the preparation of 2- chlorobutadiene-1,3 and more particularly to the preparation of this compound from products obtained by chlorinating 2-chlorobutene-2.

This application is a continuation-in-part of our copending application Serial No. 234,693, filed October 12, 1938.

2-chlorobutadiene-1,3 is a colorless liquid having an atmospheric boiling point of 59.4 C. The compound may be readily polymerized and because of this property, it has received considerable attention for use in the preparation of synthetic rubber-like products.

It is an object of the present invention to provide a convenient and practical method for preparing 2-chlorobutadiene-1,3. A further object is to provide a. method for the preparation of this compound by dehydrochlorination of products obtained by chlorinating 2-chlorobutene-2. These and still further objects will be apparent from the following description of our invention.

The above objects may be accomplished in accordance with our invention by. subjecting products which are obtained by chlorinating 2-chlorobutene-2 to pyrolysis in the vapor phase. When 2-chlorobutene-2 is chlorinated, either in the liquid or vapor phase, for example, at temperatures ranging from 0 to 125 0., products are obtained which may be readily converted to 2-chlorobutadiene-1,3 by the method of our invention. These products include 2,2,3-trichlorobutane and two isomeric dichlorobutenes boiling at temperatures of 111 to 112 C., and 130 to 131 C. Any of these three compounds or mixtures thereof when pyrolyzed in the vapor phase yields 2-chlorobutadiene-1,3. We have discovered that such pyrolysis may be eifected so as to obtain 2-chloro- 'butadiene-LB as substantially the only monochlorobutadiene reaction product.

The dehydrochlorination of 2,2,3-trichlorobutane, and the dichlorobutenes mentioned above, or mixtures-0f those compounds may be effected in the vapor phase in accordance with our invention in the presence or absence of dehydrochlorination catalysts or of diluent materials such as steam, nitrogen and the like. The use of a diluent such as steam does not appear to be particularly advantageous since excellent results may be obtained in the absence of such materials or even in the absence of catalytic materials. However, the presence of a material which catalyzes the dehydrochlorination of chlorinated organic compounds in the vapor phase, under some conditions offers certain advantages. As a. general matter, when a suitable catalyst is compounds in the vapor which boils at 111 to 112 employed, the yield of 2-chlorobutadiene=1, is

somewhat higher and the rate of formation is accelerated. r l

The various which are generally efiective in effecting removal of hydrogen chloride from chlorinated organic phase may be used successfully in practicing our invention. Of,,particular value, are the salts of alkaline earth metals, particularly alkaline earth metal halides such as magnesium chloride, bariumchloride, calcium chloride and the like. These substances are particularly effective as catalysts forefiecting the conversion of the above mentioned trichlorobutane and dichlorobutenes'. to 2-chlorobutadiene-1,3 without the formation of Joy-product monochloro-butadienes. Magnesium salts, wespecially magnesium chloride, magnesium sulfate and mixtures of the two, are particularly valuable as catalysts in that they have a desirable accelerating effect upon thepyrolysis reaction toform 2-chlorobutadiene-1,3. i

The present method may be practiced by operating at temperatures over from about 300 C. up to temperatures at which 2- chlorobutadiene-1,3 is decomposed at an excessive rate. As a general matter operation within the temperature range 400-600 C. has been found to produce good results, the temperature range of 4'70-520 C. being preferred. i

The 2,2,3-trichlorobutane which may be used as starting material in practicing the present method is a compound having an atmospheric boiling point of 141.6 to 142.8 C. and a density f 20 1.2672 v The two isomeric dichlorobutenes which may be used as raw materials include a dichlorobutene C. and has a density of and a second dichlorobutene which boils at 130 to 131 C. and has a density of These isomeric dichlorobutenes are believed to be 2,3-dichlorobutenes, probably isomers of 2,3-dichlorobutene-2. The preparation of these three compounds is described in our copending application Serial No. 336,624, filed May 22,1940. That dehydrochlorination catalysts a wide range, e..g.

. dime-1,3, or mixtures of any in theform'of amixture of chlorobutene resulting mole of hydrogen chloride therefrom through the" Z-chIorobutadiene-IB.

volving-the' liquid phase chlorination of 2-chlorobutene 2, preferably in the presence of a catalyst such as ferric chloride'or stannic chloride, whereby. mixtures of the compounds are readily obtained.- Suitable mixtures of thecompounds may also be obtained by'chlorinatlng '2-chlorobutene-Zin thevapor phase for example, at a temperature ranging from the'startingcompound to 125 C. a temperature of'*100 'to 125 C. being preferred. The liquid phase chlorination may presence of actinic light to give suitable mixtures of the abovecompounds as described in the copending application of Cass and KBurg Serial No. 336,626, flled May 22; 1940.

Any one of the'above mentioned three .compoundsm'ay be pyrolyzed to obtain 2-chlorobutatwo or more of the compounds may beused. When the'methods described in the aforementioned copending applications are-employed for preparing these compounds, the compounds are generally obtained all three compounds .althoughin some'instances, e. g. when employing stannic" chloride' as catalyst in the liquid phase, the amount of the dichlorobutene boiling at 130to' 131 C'. is small.

The-iollowing examples are specific illustrations of the present invention;

Example I 2.2,3-trichlorobutane, 244 grams, was distilled slowly, the resulting vapors being passed'con- /t inuously through an unpacked tube construct- "ed of aborosilicate glass sold under the trade .name Pyrex, this glass being characterized by its-low thermal coefllcient-of expansion and its high softening temperature. The glass tube was'heated externally to provide a temperature in the tube of 470-490 C. The-vapors issuing also be effected in the the boiling point of I temperature condenser for from thetube were fractionally condensed so' as .to separate unchanged trichlorides and dichlorides fromthe off-gases, the separated material being returned to the original distillation flask for Irecirculation ,uncondensed' 2-chlorobutadiene-1,3, together with evolved hydrogen chloride, was passed through a series of cooled water scrubbers where the desired product collected as an oil. After recirculating unreacted trichlorobutane and difrom the removal of one heated tube for a period of about three hours, thechlorobutadiene collected in the water scrubbers'w'as fractionated to determine its composition. Distillation analysisof this product showed that it contained, aside from a slight amount of high boilimg materials. comprising chiefly trichlorobutane and dichlorobutenes, only one monochlorobutadiene, which" was identified as The amount of purified through the heated tube. The

product actually isolated by distillation corresponds to a yield (if-approximately 62.5%.

Example-II served as aboiler for distilling products to be pyrolyzed into the reaction tube. The exit end of the 'tubewas fitted witha fractional condenser which served. to condenseout material not conof a liquid seal back to the distillation flask for revaporization and recirculation through the reaction tube. Connected with the above mentioned condenser was a second condenser for condensing 2-chlorobutadiene-L3, which second condenser was in turn connected with a scrubbing system for removing hydrogen chloride. Gases passing through this scrubbing system were then passed to a drier tube and finally to a lowremoving last traces of product from gases which were to be The distillation flask was charged with 1.51 moles of 2,2,3-trichlorobutane and heated so as to distill vapors of the trichloride at a uniform and suitable rate through the reaction tube. The first condenser into which the reaction products passed was maintained at a temperature such that the trichlorobutane and any intermediate dichlorobutenes formed'would be condensed from the gaseous reaction mixture, the condensed material being returned to the distillation flask, vaporized therein and recycled through the reactionv tube, After operating in this manner for 4 /2 hours while maintaining the temperature within the reaction tube at 4'70 to 490 C., the material remaining in the distillation flask amounted to about 30 grams. The crude product collected in. the second and tioned above and also in the water scrubbers, was washed with water, dried and fractionally distilled. There were obtained-0.5 moleof monomeric 2-chlorobutadiene-1,3 and 0.51 mole of dichlorobutenes consisting mostly of. a dischlorobutene boiling at 111 C. The amount of these two compounds isolated correspondedto yields of 33% and 33.8%, respectively, based upon the amount of trichlorobutaneoriginally employed.

Example III Example II, using a quartz tube in place of the I Pyrex glass reaction tube.

In starting the run, 4 moles of 2,2,3-trichlorobutane were charged into the distillation flask and during the run the temperature in the reaction tubev was maintained at 400-465 C. After operating in the manner indicated. in Example 11 for a period .of 1% hours the combined crude product from the second and third condensers and from the water scrubbers was subjected to steam distillation, dried and then fractionally distilled. There were 0btained'0.6 mole of monomeric 2-chlorobutadiene-1,3, 1.1 moles of .dichlorobutenes and 1.28 moles of unconverted 2,2,3-trichlorobutane. The yields of 2-chlorobutadiene-1,3 and dichlorobutenes corresponded to 22% and 40.5% respectively, based upon the trichlorobutane not recovered.

Example IV vented.

last condensers menvapors passed directly into the stainless steel reactor. The gaseous reaction products were passed from the reactor to a cold water conand fractionated through a packed column 4 feet long. 1

During the course of the run 11.5'moles of 2,2,3-trichlorobutane were passed into the vaporizer at a rate of about 5 to 6 cc. per minute, the vaporizer being held at a temperature of 280 to 310 C. The product obtained from the steam distillation of the crude reaction products weighed 1324 grams after having been dried. Upon subjecting this crude product to fractional distillation there was obtained 1.8 moles of monomeric 2-chlorobutadierie-L3, the remainder consisting chiefly of dichlorobutenes and unconverted 2,2,3-trichlorobutane. This unconverted material, including the dichlorobutenes. was again passed through the reactor under the same conditions as described for the'first pass. From of materials obtained by chlorinating 2--chlorobutene-z in the presence of light at C. was used as starting material. The compositionof the starting material was 116 grams (1.28 moles) oi 2-chlorobutene-2, 393 grams (3.15 moles) of dichlorobutene, 179 grams (1.11 moles) of 2,2,3-

trichlorobutane and 64 grams of high boiling materials. The temperature of the reactor tube was maintained at480-500 C. and after. operating for a period of 3% hours 626 grams of crude product were obtained. The product obtained from a single pass through the reactor was washed, and then subjected torapid distillation whereby there was isolated 577 grams of distilled, mixed products. The '2-ch1orobutadiene-L3 .was isolated from this mixture of products as spay merby subjecting the mixture to'polymerization in the presence of benzoyl peroxide, the. polymerization treatment being followed bya, steam distillation treatment to remove and "recover volatile products. There wereisolatedby means of this procedure 1.56 moles of polymerized '2- chlorobutadiene-1,3, 2.3 moles of. dichlorobutene and 0.2 mole of 2,2,3-trichlorobutane. The amount of 2-chlorobutadiene-1,3 isolated in'the form of its polymer, corresponded to a yield of the second pass there were obtained 717 grams'of dried crude product after steam distillation. Fractional distillation of this material yielded an additional 1.46 moles of monomeric 2-chlorobu- 'tadiene-1,3 and 5 moles of a, mixture of dichlorobutenes containing approximately equimolar quantities ofthe two isomers boiling at 111 and 130 C. Also obtained were 0.8 mole of uncon verted triochlorobutane'and 103 rams of high boiling material. The- -ov'er-all amounts of 2- chlorobutadiene-Lfi and of dichlorobutenes obtained corresponded to yields of 30.5% and 47%, respectively, ,based upon unrecovered 2,2,3-trichlorobutane. The yield of z-chlorobutadiene- 1,3 based upon 2,2,3-trichlorobutane not recovered as such or as dichlorobutenes was 57.2% of the theory.

example were essentially the same as described in Example III. The experiment was carried out, however, using as the starting material 3 moles of the dichlorobutene isomer boiling at 111- 112 C. Four grams of phenol were added to the starting material, the purpose of the phenol being to inhibit polymerization of the desired product. The temperature in the quartz reaction tube was maintained at 410-430 C during the course of the experiment The dichlorobutene was vaporized and passed through the reactor tube during the course of 2 hours, during which time the boiling point of the dichlorobutenein the distillation flask rose from 111 C. to about 135 C. There were isolated from the reaction product, employing the method described in the foregoing examples, 0.91 mole of monomeric 2-chlorobutadime-1,3 and 1.1 moles of unconverted dichlorobutene. The yield of 2-chlorobutadiene-1,3 was 48% of the theory based upon the unrecovered dichlorobutene.

ample were essentially the same as described in Example IV except that 752 grams of a mixture 88.5% based upon the unrecovered tene and trichlorobutane.

Erample VII dichlorobuchlorobutadiene-1,3, 2.8 moles of dichlorobutene and 0.26 mole of 2,2,3-trichlorobutene. The yield of 2-chlorobutadiene-1,3 was 42% based upon the unrecovered dichlorobutene and trichlorobutane.

Example VIII The apparatus of this example was essentially the same as that described in Example II except that a quartz reactor tube was used and no provision was made for recycling unconverted products. The quartz tube was packed with carbon impregnated with barium chloride which served as a catalyst. During the course of 1% hours, 3 moles of 2,2,3-trich1orobutane vapor were passed through the reaction tube which was held at a temperature of 290-300 C. The crude reaction product was washed with water, dried and fractionally distilled to give 0.45 mole of monomeric 2- chlorobutadiene-1,3, 1.19 moles of dichlorobutenes (boiling at 101 and 131 C.) and 1.06 moles of unconverted 2,2,3-trichlorobutane. The amount of 2-chl0robutadiene-1,3 isolated corresponded to a yield of 60% based upon the trichlorobutane not recovered as such or as dichlorobutene.

The present method is well suited for practice on a commercial scale inasmuch as it is simple and results in good conversion of the starting materialto the desired product. The fact that no monochlorobutadiene other than 2-chlorobutadime-1,3 results from the process is particula l advantageous in that it is possible to obtain the desired product in substantially pure form with out employing elaborate purification methods. It

may be desirable in the normal operation of the 7 present process on a commercial scale to add small amounts of materials to the substances being pyrolyzed, which materials are effective-in inhibiting polymerization of 2-chlorobutadienel,3. As examples of such materials are mentioned amines, phenolic compounds and the like sub- I stances.

The product obtained by the present method may be polymerized to produce various rubberlike products whichare highly useful for various purposes. The method may be practiced employing reaction tubes made ofvarious construction materials such as glass, iron, nickel, copper or stainless steel. Operation at atmospheric pressure is convenient; however; pressures either above or below atmospheric pressure-maybe employed in accordance with our invention.

h As many widely different modifications of the present invention maybe practiced without departing from the spirit and scope thereof, it is to be understood that the inventionis not to be limited by the foregoingdescriptionand examples, which are intended merely to be illustrative of the invention, except as indicated in the appended claims.

We claim: I

1. A method of preparing 2,-ch-lorobutadiene- 1,3 comprising subjecting 2,2,3-trichlorobutane to vapor phase pyrolysis at :a temperature of 300 to 600 C.

" *2. A method of preparin z-chlorobutadiene- 1,3 comprising subjecting 2,2,3-trichlorobutane to vapor phase pyrolysis at a temperature ,of 470- 520 C.

3. A method of preparing 2-chlorobuta'diene- '1,3 comprising subjecting2,2,3-trich1orobutane to vapor phase pyrolysis at a tempera'ture' of 300 to 600 C. in the presence of a dehydrohaloge'nation catalyst. 1 i

4. A method or preparing z-chlorobutadiene- 1,3 comprising subjecting 2,2,3-trichlorobutane to vapor phase pyrolysis at a temperature of 300- 600 C. in the presence of a salt of an alkaline earth metal. 1 1

5. A method of preparing 2-chlorobutadiene- 1,3 comprising subjecting 2,2,3-trichlorobutane to vapor phase pyrolysis at a temperature of 300 to 600 C. in the presence of a, magnesium salt.

6. A method of preparing 2-chlorobutadiene- 1,3 comprising subjecting 2,2,3-trichlorobutane to vapor phase pyrolysis at a temperature of at least 400 C.

7. A method ,of preparing 2-chlorobutadiene- 1,3 comprising subjecting the mixed product obtained by chlorinating 2-chlorobutene-2 to vapor phase pyrolysis at a temperature of at least 400" C.

8. A method of preparing Z-chIorobutadiene- 1,3 comprising subjecting the mixed product obtained by chlorinating 2-chlorobutene-2 to vapor phase pyrolysis at a temperature of 300 to 600 C.

ARTHUR A. OLIVER W. CASS.

REFERENCUES' CITED Thefoll'owing references are of record in the file of this patent:

UNITED STATES PATENTS Date (Abstract of article by Klebanskii et al., in J our.

Applied Chem. U. S. S. R., vol. 9, 1936, pages 1985- 

